The use of microorganisms such as fungi or bacteria for biological control in agriculture is known in the art. For example, microorganisms may be used for the improvement of crop growth and protection of plants in agriculture. Plant growth-promoting bacteria are disclosed for example in Bashan, 1998 (1). There are various factors limiting the effectiveness of biological control of microorganisms in agriculture, such as for example sensitivity of the microorganisms to UV radiation present in the field (2, 3). Moreover, direct use of antibiotics derived from biocontrol agents is limited due to UV sensitivity (4, 5).
The use of alginate gel technology to formulate agricultural products, pesticides, and food items is known in the art. For example, U.S. Pat. No. 4,053,627 describes the use of alginate gel discs for mosquito control, U.S. Pat. No. 3,649,239 discloses fertilizer compositions, and U.S. Pat. No. 2,441,729 teaches the use of alginate gels as insecticidal as well as candy jellies. In addition. U.S. Pat. Nos. 4,401,456 and 4,400,391 disclose processes for preparing alginate gel beads containing bioactive materials. None of these patents teaches the use of viable microorganisms as an active material incorporated in an alginate matrix.
U.S. Pat. Nos. 4,767,441, 4,818,530 and 4,724,147 disclose alginate gel pellets containing viable fungus capable of producing conidia when exposed to sufficient light and moisture. The resultant alginate gel pellets can then be dried and used to inoculate agriculture fields to kill selected plant pathogens. The alginate carrier disclosed in these patents comprises condensed pellets which lack a porous structure which is conducive to achieve optimal release of the active microorganisms or diffusion of active products produced by these microorganisms in field conditions. Furthermore, none of these patents disclose the incorporation of biological control bacteria in the alginate pellets.
One of the inventors of the present invention previously disclosed sponge-like, dry alginate beads obtained by freeze-drying alginate-based gel beads or other gels produced from water-soluble polymers (6 and U.S. Pat. No. 6,589,328). Freeze-drying of gel beads results in a low-density dried cellular product that is composed of many fused open and closed cells (compartments). The freeze-drying process creates the cell wall that contributes to the bead's mechanical properties and immobilization ability (7, 8). It was further disclosed by one of the present inventors that it is possible to preserve chitinolytic Pantoae agglomerans in a viable form by cellular dried alginate-based carriers (9).
There is an unmet need in the field of biological control for carriers of viable microorganisms effective in controlling plant pathogens which will permit efficient extended release of the viable microorganisms to the surrounding ground and which will protect the microorganisms against UV radiation.